This proposal describes a series of experiments designed to examine bradykinin receptors in kidneys from normotensive and hypertensive rats. The approach to be taken will employ 125I-tyr1 kallidin as a bradykinin receptor probe in order to study directly the interactions between bradykinin and its receptors. 125I-tyr1 kallidin binding will be characterized with respect to its affinity and specificity and with respect to the effects of pH and ionic composition. To minimize the possibility of non-receptor, bradykinin binding proteins, e.g. kininases, interfering with this study of bradykinin receptors, the receptors will be partially purified using column chromatographic techniques until they are separated from all demonstrable kininase activities. Porcine kidneys will serve as the receptor source for experiments in which the conditions for receptor purification will be determined. Conditions used to purify kininase II to homogeneity will be tried first to see whether they will also be suitable in receptor purification. The binding of 125I-labeled bradykinins to purified kininase II from porcine kidney will also be studied in order to be able to clearly differentiate this binding from receptor binding. When experiments with porcine kidneys are completed, experiments with rat kidneys will begin. Kidneys from spontaneously-hypertensive rats of the Wistar-Kyoto strain and from salt-sensitive rats of the Dahl strain will be used in these experiments. Questions to be addressed in this project include: Are there differences in the numbers and/or affinities of bradykinin receptors in kidneys from normotensive and hypertensive rats? Are there naturally occurring bradykinin receptor blockers in kidneys from hypertensive rats but not from normotensive rats?